PMBCL is an acquired cancer that develops when a thymic B-cell undergoes genetic and signaling changes, allowing it to grow without the normal controls that limit cell division. It is not an inherited condition; people are not born with PMBCL, and it does not run in families in a predictable pattern. Researchers have described recurrent biological features in PMBCL, including activation of certain growth and survival signaling pathways and immune-evasion mechanisms, but these are changes that arise within the affected cells over a person's lifetime rather than mutations passed down from parent to child. The reasons a particular person develops PMBCL are not fully understood, and no single environmental or lifestyle cause has been established.

Diagnosis of PMBCL begins with imaging, typically a chest X-ray and computed tomography (CT) scan, which reveal an anterior mediastinal mass. Definitive diagnosis requires a tissue biopsy, often obtained through a core needle or surgical approach, with review by a hematopathologist. Microscopic examination shows large lymphoid cells with characteristic compartmentalizing fibrosis. Immunohistochemistry helps confirm B-cell lineage and distinguish PMBCL from other mediastinal tumors and from classical Hodgkin lymphoma, which can look similar. Once the diagnosis is established, staging is performed with whole-body imaging, most often a positron emission tomography (PET)-CT scan, along with laboratory tests and, in selected cases, a bone marrow evaluation. Diagnosis and staging are best coordinated through a specialized center.

Treatment of PMBCL is planned by a multidisciplinary oncology team and depends on individual factors such as disease extent, age, and overall health. Initial therapy generally combines intensive chemoimmunotherapy regimens that pair chemotherapy with an antibody directed against B-cells, sometimes followed by consolidation radiation therapy to the mediastinum. The goal of upfront treatment is typically curative. For disease that does not respond to first-line therapy or relapses afterward, additional options may include further systemic therapy, autologous or allogeneic stem cell transplantation, and immunotherapy approaches. Several FDA-approved cell therapies and immune checkpoint therapies have received approval for use in the relapsed or refractory setting. Treatment plans, including eligibility for any specific therapy, should be discussed in detail with the care team.

Outcomes in PMBCL have improved significantly with modern combined treatment, and many people achieve long-term remission after initial therapy. Prognosis depends on factors including disease stage at diagnosis, response to first-line treatment, age, and overall health. Patients whose disease responds well to upfront chemoimmunotherapy often have favorable long-term outcomes, while disease that does not fully respond or that relapses can be more challenging to treat. Individual response to therapy varies, and survival statistics from older studies may not reflect current results given recent advances in treatment. Early diagnosis and access to specialized hematology-oncology care are important contributors to outcomes. Long-term follow-up is recommended to monitor for late effects of treatment and for any signs of relapse.

PMBCL is an active area of research, with numerous ongoing clinical trials investigating new and refined treatment strategies. Studies are exploring novel chemoimmunotherapy combinations, bispecific antibodies, immune checkpoint approaches, and chimeric antigen receptor (CAR) T-cell therapies, as well as efforts to reduce long-term toxicity, including approaches that may avoid radiation in selected patients. Recent published research includes case series, reviews, biomarker studies, and reports linked to ongoing trials, reflecting strong investigator interest in this distinct lymphoma. Individuals interested in learning about clinical trials can search ClinicalTrials.gov or speak with their care team about whether a research study might be an option for their situation.